Making registrar back to public

Author: Manny Jimenez

firebase-app-distribution/src/main/java/com/google/firebase/app/distribution/FirebaseAppDistributionRegistrar.java

@@ -33,7 +33,7 @@
  * @hide
  */
 @Keep
-class FirebaseAppDistributionRegistrar implements ComponentRegistrar {
+public class FirebaseAppDistributionRegistrar implements ComponentRegistrar {
 
   private static String TAG = "Registrar:";